While analysing the output of #13861 I stumbled over an unnecessary pessimisation in handling of scrutinised values. With words of Simon (from https://phabricator.haskell.org/D4267 with minor edits added):

Interesting. Yes, please make a ticket! (And transfer the info below into it.)

I think the issue is this. Given (the STG-ish code)

data Colour = Red | Green | Blue
f x = case x of y
           Red -> Green
           DEFAULT -> y

(here y is the case binder) we can just return x rather than entering it in DEFAULT branch, because y will be fully evaluated and its pointer will be correctly tagged.

You absolutely can't check for an OccName of "wild"!! That is neither necessary nor sufficient :-).

Instead, check isEvaldUnfolding (idUnfolding y). See Note [Preserve evaluatedness] in CoreTidy.hs. And be sure to augment that note if you make the change.

I would expect perf benefits to be small on average, but it's simple to implement.